With popularization of network technology represented by the Internet, improvement in network stability becomes imperative. Network reliability is improved by redundantly configuring a node apparatus and a link constituting the network beforehand and performing dynamic path control. In a network in which the dynamic path control is performed, node apparatuses constituting the network exchange information relating to each other's connection status, and autonomously decide an optimum path based on these pieces of information. For example, when there is a failure in a link connecting to its own apparatus or an adjacent node apparatus, a node apparatus having detected the failure informs other node apparatuses of this matter. Accordingly, all the node apparatuses in the network perform path calculation in a state with the node apparatus or link having the failure being excluded, to decide a new path. Thus, even if a failure occurs, the dynamic path control enables communication service to be maintained continuously by only the remaining node apparatuses and links.
In Patent Document 1, the following method has been proposed. A node installed in the network self-calculates or acquires tree information of the network from other nodes to ascertain the tree information. The node extracts beforehand a set of nodes that includes an input/output link of the own node as a part of the tree, as an extent of the impact of a link failure, based on the ascertained tree information. The node notifies detection of the failure, limiting to the extent of the impact, when having detected the link failure. When the own node detects the failure, or receives the notification from another node, the node recalculates the path.
In order to realize such dynamic path control, a path control protocol as shown in Non-patent Document 1 has been standardized by the Internet Engineering Task Force (IETF), which is a standard-setting organization.